Carvedilol, chemically known as (±) 1-(9H-carbazol-4-yloxy))-3-[2-(2-methoxyphenoxy)ethyl]amino-2-propanol, (CAS Registry No. [72956-09-3]), having following structural formula (I)

Carvedilol having structural formula (I) is a nonselective β-adrenergic blocking agent with α1 blocking activity.
Carvedilol has an asymmetric carbon and exists either as individual stereoisomers or in racemic form. The nonselective β-adrenergic activity of Carvedilol is present in the S(−) enantiomer and α1 blocking activity is present in both the R(+) and S(−) enantiomers at equal potency. It is marketed in racemic form.
EP 0127099 describes the preparation of both the racemate and stereoisomers. U.S. Pat. No. 4,503,067, U.S. Pat. No. 4,824,963, EP 0127099, EP 918055, EP 1142873, WO 02/00216 patents incorporated herein by reference discloses various processes for preparing Carvedilol.
U.S. Pat. No. 4,503,067 discloses a process for preparation of Carvedilol by the following reaction scheme-I.

4-(oxiran-2-ylmethoxy)-9H-carbazole (II) is reacted with 2-(2-methoxyphenoxy)ethylamine (III) in a molar ratio of 1:1.1 and the reaction was carried out at 50° C. temperature for 25 hours. The process gives low yield of 39.42%. A considerable amount of by-product (formula IV) is formed, resulting in a low yield of desired product and making the purification difficult.

EP 918055 A1, EP 1142973 A2 discloses the preparation of Carvedilol as mentioned in scheme-II

The process involves the catalytic N-debenzylation at the final stage. According to literature knowledge, N-debenzylation reaction never goes for 100% completion, leading the traces of N-benzyl Carvedilol (VI) as major impurity in final product. The European pharmacopoeia has covered the limit of this impurity (VI) not more than 0.02% due to its toxic nature and practically it is very difficult to achieve this level by the process based on scheme-II.
Recently US 2002/0143045 A1 discloses the preparation of Carvedilol by reaction of 4-(oxiran-2-ylmethoxy)-9H carbazole (II) with 2-(2-methoxyphenoxy)ethylamine (III) in 1:1.5 to 1:100 molar ratio without solvent in neat condition at 100° C. to minimize the formation of compound (IV) as by-product. This patent does not disclose the yield and the purity of the Carvedilol obtained. At higher temperature, in the absence of solvent there is possibility of degradation that results in low yield. Also the use of large amount of 2-(2-methoxyphenoxy)ethylamine (III) makes the process uneconomical.
It is evident from above that though prior art looks conceptually very good, but practically it is very difficult to implement at large scale production. According to the U.S. Pat. No. 4,503,067, the reaction time itself is 25 hours with lesser yields. While in WO 02/00216 the product is crystallized out in 40 hours at 4° C. and according to the European Patent EP 918055, the final stage involves catalytic hydrogenation for debenzylation. Thus these processes are not feasible on production scale.